Data extraction

Characteristics of the included studies are presented in Table 2 which summarises the extracted details on study methodology (i.e., final sample size at follow-up, participants' characteristics, sleep assessment measure, outcome assessment measure, number of follow-up assessments and duration of follow-up, adjusted variables, and main results on the effect of changes in sleep on outcome measure). For studies with multiple outcome measures, the main results included in this review were those related specifically to the effect of change in sleep on a pain-related health outcome. When the relevant information was missing or not reported in the preferred formats in the original paper, the corresponding author of the article was contacted by email, with another follow-up email sent after three weeks if no response. Requests were sent out requesting additional information for seven [36], [37], [38], [39], [40], [41], [42] of the included articles. Five authors responded and three [36], [40], [42] were able to provide the requested information.

Study characteristics.

BMI: body mass index, CES-D: center for epidemiological studies depression scale, CI: confidence interval, CRP: creatinine reactive protein, HR: hazard ratio, ICSD: international classification of sleep disorders, IL-6: interleukin-6, MCS: mental component summary, NKCA: natural killer cell activities, OR: odds ratio, PCS: physical component summary, POMS: profile of mood states, PSG: polysomnography, PSQI: Pittsburgh sleep quality index.